326 Introduction to Animal Morphology. 



placed fins ; mantle united by hinge cartilages, linear 

 or dilated, not by muscle ; arms united by membrane ; 

 funnel short, with no valve ; shell long, slender ; tenta- 

 cles non-retractile. Thysanoteuthidoe — long or oval ; arms 

 free ; inner shell auricled at base, or hastate. Onychoteu- 

 thidae — long, cylindrical ; eyes with a wide corneal open- 

 ing and a sinus above ; arms with hooks along their margin ; 

 funnel with a valve ; shell dilated at both ends (Enoploteu- 

 this), in front with one central and two lateral ribs (Omma- 

 strephes). Sub-order 2. Octopoda(Zraf/i) — arms eight, with 

 sessile suckers, each without a cuticular ring ; body short, 

 roundish ; mantle usually without a hinge cartilage ; oviduct 

 paired ; nidamental gland none. This includes Cirrhotcu- 

 thidae — arms united by membrane to tip : body soft, with 

 round fins ; a cartilaginous inner shell ; the suckers alternate 

 with cirrhi, Octopodidse — mantle joined to the visceral sac 

 by a broad muscle at the median line ; shell and water pores 

 none ; suckers short, in one (Eledone) or two rows (Octopus). 

 13. Philonexidas — mantle with a cartilaginous, button-like hinge 

 apparatus, and many water pores ; suckers fleshy, peduncled ; 

 arms all free (Philonexis), or two of them webbed (Tremocto- 

 pus). Argonautidce — arms subulate, the two upper webbed 

 at end, and secreting a shell in the female ; mantle hinge 

 apparatus as in last ; male much smaller than female. 



The gigantic pelagic forms, krakens of the Scandinavians, 

 belong to Onychoteuthids, and form the genus Architeuthis 

 of Steenstrup. The arm of one of these, driven on the west 

 coast of Ireland in 1875, measured thirty feet in length. 



